The present invention relates to a semiconductor circuit, and more particularly to a semiconductor circuit in which a power line which is supplied to a circuit having an oscillating circuit and a circuit having no oscillating circuit is divided into two lines.
For, example, in a semiconductor circuit having a switching regulator of the charge pump type therein, there is conducts a high-speed switching operation and other circuits are arranged on one chip. In a circuit of this type, there is a case in which a noise propagated from the circuit that conducts the high-speed switching operation through the power line occurs in other circuits.
Under these circumstances, until now, the power line which is supplied to the circuit that conducts the high-speed switching operation and the power line which is supplie to the circuit that conducts a low-speed switching operation are divided, to thereby reduce the noise which is propagated from the circuit that conducts the high-speed switching operation.
In the case where a semiconductor device is large in size, a floating capacitor C occurs in the wiring of the divided power circuits, and a wiring resistor R and the floating capacitor C make it possible to reduce the noise propagation caused by the high-speed switching operation.
However, in case of a semiconductor circuit a chip size of which is, for example, about 2 mm square, because the wiring per se of the power circuit is shortened, a sufficient floating capacitor C and wiring resistor R cannot be obtained with the result that a time constant becomes small, and the propagated noise caused by the high-speed operation cannot be sufficiently reduced by merely dividing the power line.
In view of the above, an object of the present invention is to provide a semiconductor circuit which is capable of sufficiently reducing the propagated noise caused by the high-speed switching operation even if the semiconductor circuit is downsized.
According to the present invention, there is provided a semiconductor circuit, comprising: a first circuit having an oscillating circuit for conducting a switching operation at a high speed; a second circuit having no oscillating circuit; a power terminal connected with a power supply; a first power line for connecting the power terminal and the first circuit to each other; a second power line for connecting the power terminal and the second circuit to each other; and a resistor disposed on at least one of the first power line and the second power line. The provision of the resistor on the power line permits a high-frequency noise the occurs in the first circuit and is propagated to the second circuit through the power line to be reduced.
It is preferable from the viewpoints of a voltage drop due to the resistor and the arrangement of the resistor that the resistor is disposed on each of the first power line and the second power line, and the resistances of both the resistors are identical with each other.
Also it is preferable from the viewpoint of a reduction of power loss that the resistor is disposed on each of the first power line and the second power line, and the resistances of the respective resistors have such values that electric energy consumed in the first circuit and the second circuit within a given period are equal to each other.
Further, it is preferable that the resistor is formed of a polysilicon resistor.
Still further, the first circuit may be formed of a DC-DC convertor circuit of the charge pump type.